German patent specification DE 260030 discloses a so-called double-girder gantry crane having two horizontal crane girders and two vertical support girders which form a gantry frame of the gantry crane. The crane girders extend in parallel and at a spaced interval with respect to each other. Arranged at each of the lower ends of the support girders is a travelling mechanism, by means of which the gantry crane can be moved in a direction of travel extending transversely with respect to the longitudinal direction of the crane girders. A crane trolley having a cable winch can be moved on and along the crane girders. According to the design as a double-girder crane, a load picking-up means of the cable winch arranged on the crane trolley is lowered or raised between the two crane girders. The crane girders are formed as trussed girders and comprise in each case an upper run and a lower run which are each oriented horizontally and in parallel with each other. The upper and lower runs of the two crane girders are connected to one another by means of vertically extending, rod-shaped posts and diagonally extending, rod-shaped struts. The two crane girders are connected to one another at their ends by means of transverse rods and struts to form a frame. Rod-shaped posts and struts are provided along the longitudinal direction of the crane girders between the upper and lower run as a type of truss and each connect an upper run to the lower run arranged vertically therebelow.
German utility model document DE 1 971 794 U describes a double-girder overhead crane whose two horizontal crane girders are connected to one another by means of head girders arranged at the respective ends thereof and can be moved together in a direction of travel extending transversely with respect to the longitudinal direction of the crane girders. Both crane girders are designed in a similar manner as trussed girders and comprise in each case plate-shaped upper runs, rod-shaped lower runs and rod-shaped posts.
German laid-open document DE 2 239 573 A discloses a trussed girder, of which the upper run and the lower run are connected together via struts. The struts are designed as angle profiles, of which the lower ends comprise a slot and are screwed to the lower run.
German patent specification DE 10 95 486 B discloses a crane girder which is designed as a trussed girder and of which the struts which connect the upper run and lower run to one another are formed by rod-shaped T-profiles. The rod-shaped struts comprise at their ends recessed flanges with which they lie against the upper run in the manner of a joint, whereas the webs lie on the upper run.
European patent application EP 0 928 769 A1 describes a crane girder which is designed as a trussed girder, against the upper run and lower run of which angular struts having an L-shaped cross-section lie. The L-shaped cross-section of the angular struts is formed by a main surface extending in the longitudinal direction of the crane girder and by an auxiliary surface adjoining thereto and folded by 90 degrees. The auxiliary surface comprises an aperture which is arranged in the region of the upper run.
U.S. Pat. No. 7,503,460 B1 discloses a crane girder which is designed as a trussed girder and has rod-shaped struts composed of two strut profiles. In this case, the strut profiles are arranged spaced apart from one another by spacers. In each case, a plate connected to an upper run or a plate connected to a lower run is pushed and welded between the ends of the strut profiles.
Chinese document CN 202 465 064 U also discloses composite struts of a trussed girder which each comprise a pair of mutually spaced apart U-profiles. The U-profiles are fastened on both sides with their ends to a plate-shaped web of the lower run which is arranged between the ends of each pair of U-profiles.